Mathematical Modeling of Biodiesel Production under Intense Agitation

In this study, a new approach is proposed to investigate the kinetics of sunflower oil and rapeseed oil transesterification in the presence of potassium hydroxide. Transesterification is a heterogeneous process which affected by a number of parameters, that are not readily available in the literature, such as mass transfer coefficients, partition coefficients, and specific surface area of the dispersed phase. However, under intense agitation condition, mass transfer restrictions may be neglected, and the two phases are supposed to remain in thermodynamic equilibrium, during the process. Therefore, a model was developed independent of the mass transfer coefficient and specific surface area, which is reliable for the intense agitation condition. According to the results, the model is valid at least for mixing rates over 500 rpm. The results of the model were used to study the effects of temperature, methanol-to-oil ratio, and catalyst concentration on the biodiesel conversion. Biodiesel production rate increases with increasing temperature, although rapeseed oil transesterification is more temperature dependent. The results show that the maximum amount of catalyst concentration is less than 1% (by weight); however, the optimum value depends on the operating temperature. The optimum value of the methanol-to-oil-ratio decreases with increasing temperature. Thus, at higher temperatures, less amount of methanol and catalyst are required, which leads to easier purification of biodiesel.

Experimental and CFD Characterization of Gas Dispersing Asymmetric Parabolic Blade Impellers

Enhanced operating performance can be obtained by combining the design characteristics of impellers. The asymmetricity of BT6 impeller blades when combined with symmetric ICI gasfoil blades results in two new diskless impeller designs, one with extension of the upper blade part (PBIUP) and the other with lower blade part (PBIDN). These impellers are experimentally characterized at intense agitation and sparging conditions for power draw, gas holdup and transition regimes. CFD modeling is used to evaluate the performance of impellers based on the pressure distribution and cavity formation on and around the impeller blades. Cavity formation on the new impellers is found to be higher as compared with ICI impeller but lower than BT6. The maximum experimental power drop at intense gas flow and agitation conditions for PBIUP and PBIDN is found to be 14% and 22% as compared to power drop of 10% for ICI gasfoil and 25% for BT6. The coalescence regions, identified from predicted gas holdup profiles, confirmed the experimental observations regarding the formation of larger bubbles in the tank. Overall, PBIUP is found to give uniform gas dispersion as compared to other impellers along with the desired objective of lower power drop.

Sur l'existence de sediments oolithiques dans les gres dolomitiques du Trias (inferieur?) de Lorraine

Dolomitic oolites are reported from sandstones and dolomites of the Triassic Voltzia sandstone formation (lower Triassic?) in the axial zone of the Hunsrueck anticline near Sierck, in Lorraine, France. The presence of oolitic structures formed in an environment of small-scale but intense agitation, as is evidenced by the pulverization of associated vegetable matter, suggests the new concept that the epicontinental sedimentation took place in the vicinity of a zone of active marine sedimentation.